Reliable all-round detection of the smallest protrusions in transport containers

Description

In transport containers (trays), large objects – but small parts as well – can protrude and cause problems during the further picking process. The trays must therefore be inspected on all four sides. The requirements are high here: with a length of 600 mm transverse to the transport direction and a width of 50 mm, the inspection area is very large. Even the smallest objects, which protrude by just 1.5 mm in length and 1 mm in width, must be reliably detected in this very large inspection area. These may be dark, light and even reflective objects. The exposure time must be very short, since the inspection takes place as the container passes through and no ambient light shielding is possible. The evaluation time should be less than 100 ms. The conventional approach, which uses multiple sensors or a high-resolution, measuring light barrier for the analysis, is too complex and expensive for this detection task with very small objects.

Solution

For the lateral inspection (left and right), one LPS 36 light section sensor is used on each side. For the front and rear sides, the LSIS 412i smart camera is used. It is used there both to check for protruding objects as well as for the precise evaluation of the object sizes. If an object protrudes beyond the tray edge, the smart camera returns a signal for ejection. For the check, it uses its integrated homogeneous illumination. As a result, no background lighting is necessary – an economical reflective tape (no. 7) is fully sufficient for an unambiguous evaluation of the protruding object with the low contrast difference which exists here. Due to the very large depth of field of the smart camera, the unambiguous evaluation of very small objects is possible even with various tray heights and distances to the camera. With inspection times of 30 ms and a result rate of 30 evaluations per second, it is very well suited for fast processes, such as here as trays pass by. The smart camera checks the entire width of the tray and uses digital inputs/outputs, an RS- 232 or Ethernet interface to precisely and reliably display protruding objects at the trigger time.